The alkoxylation of alkyl groups is a standard chemical reaction in which—depending on the alkylene oxide used—ethylene, propylene and/or butylene oxide adducts of the compounds containing hydroxyl groups are formed. The alkoxylation can even be applied to complex chemical compounds, such as sugar and starch derivatives, providing they contain free hydroxyl groups.
The alkoxylation reactions of complex compounds such as these generally take place at elevated temperatures using a catalyst and in the absence of water.
According to U.S. Pat. No. 3,737,426, the reaction of starch with ethylene glycol is followed by alkoxylation with ethylene oxide and/or propylene oxide in the absence of water at ca. 170° C.
U.S. Pat. No. 3,640,998 recommends carrying out the alkoxylation at 100 to 200° C. using basic catalysts in order to minimize the decomposition of starch. This is a standard alkoxylation reaction in which atmospheric oxygen and water are always removed beforehand.
Finally, reaction mixtures of alkoxylated alkyl mono- and polyglycosides prepared by alkoxylation at 120 to 170° C. using a basic catalyst under substantially water-free conditions are known from U.S. Pat. No. 4,834,903. It is expressly emphasized in this document that the water content of the reaction mixture must be below 5% by weight and preferably below 1% by weight.
The absence of water during the alkoxylation reaction is regarded among experts as absolutely essential because it has hitherto been assumed that the water present in the reaction mixture is responsible for, or influences the amount of, the unwanted secondary product, polyalkylene glycol, formed during the alkoxylation.
However, alkyl polyglycosides are commercially available almost exclusively as water-containing preparations because alkyl polyglycosides and particularly alkyl polyglucosides are highly viscous and barely flowable in water-free form. The commercially available water-containing preparations generally have water contents of at least 10% by weight and, normally, even higher.
If, therefore, alkyl polyglycosides are to be alkoxylated, the water present in commercially available water-containing preparations of the alkyl polyglycosides ought to be removed or reduced to a content of less than 5% by weight before the alkoxylation. However, the removal of water from alkyl polyglycosides is a time-consuming and expensive process which, in addition, is difficult to carry out on a commercial scale on account of the intensive foaming involved in the removal process.
Accordingly, the problem addressed by the present invention was to provide a new process for the alkoxylation of alkyl polyglycosides in which there would be no need to remove water from the alkyl polyglycoside preparations used. At the same time, the reaction product obtained after the process would contain at most small quantities of the unwanted secondary product, polyalkylene glycol.